Overload-detecting mechanism for a lift truck

ABSTRACT

In a load-handling truck the load is accepted by a ram that is mounted on a support of the truck frame adapted to deflect slightly under the stress of the load against the ram. This deflection of the support is amplified through a multiplying lever mechanism using as fulcrums a part of the support and a fixed part of the truck so spaced from the support that it is not affected by the load. The multiplied movement is used to actuate a control or signals.

United States Patent [72 I Inventor John J. Pachter Harvey 111.

21 Appl No 782,529

[221 Filed Dec. 10,1968

[45] Patented July 6, 1971 [73] Assignee Eaton Yale & Towne Inc.

Cleveland. Ohio [54] OVERLOAD-DETECTING MECHANlSM FOR A LIFT TRUCK 7 Claims, 10 Drawing Figs.

[52] U.S.Cl .1 214/673 [51 1 Int. Cl B661 9/20 [50] Field of Search 214/670- [56] References Cited UNITED STATES PATENTS 3,031.094 4/1962 Arnot t 4 v 1 214/674 3,032,221 5/1962 Carliss et al. 214/673 3,203,672 8/1965 Santos 214/673 X 3.476,269 11/1969 Baker et al 214/2 Primary Examiner-Gerald M. Forlenza Assistant Examiner-Raymond B. Johnson Attorney-Teagno and Toddy ABSTRACT: In a load-handling truck the load is accepted by a ram that is mounted on a support of the truck frame adapted to deflect slightly under the stress of the load against the ram. This deflection of the support is amplified through a multiplying lever mechanism using as fulcrums a part of the support and a fixed part of the truck so spaced from the support that it is not affected by the load. The multiplied movement is used to actuate a control or signals.

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OVERLOAD-DETECTING MECHANISM FOR A LIFT TRUCK BACKGROUND OF INVENTION 1. Field of Invention This invention relates to an overload-detecting mechanism, and particularly, to a type of overload mechanism that is particularly adapted for use on an industrial truck.

2. Discussion of the Prior Art In the conventional industrial truck adapted to lift and move a load, a load carriage, which may take the form of load forks, is supported for vertical movement on a vertically extending upright mast assembly. Generally, this vertical movement is contributed by a hydraulic ram. The mast assembly is bodily mounted in many trucks for fore-and-aft tilting movement, whereby to stabilize a load positioned on the carriage, so that the load may be transported effectively and without danger. This tilting movement of the mast and the load is effected by operation generally of a ram that is interconnected between the mast and the main frame of the truck. The load carriage extends forwardly of the truck and its front wheels, in order that a load may be applied to the carriage. Obviously, therefore, when a load is applied to the carriage, it tends to tilt the truck about the front wheels as a fulcrum point, and it is necessary therefore to design the truck so that this tilting movement of the load about the forward wheels is balanced by the weight of the truck.

Balancing of the load in this manner, frequently requires the use of a relatively heavy counterweight at the end of the truck opposite the mast. However, because there is a tendency for operators to overload a truck of the particular class, the counterweight is frequently overbalanced, with considerable damage to the truck and injury to the operator.

Manufacturers of industrial trucks and similar vehicles have long been aware of the danger inherent in overloading, and numerous contributions have been made of mechanisms that will prevent the use of overloaded vehicles. However, so far as I know, while many of these mechanisms have considerable utility, none has actually proven fully effective.

One overload prevention system is found in the Carliss U.S. Pat. No. 3,032,221, issued May 1, l962. In that patent, there is shown a weight-sensitive mechanism embodied in a structure utilized for tilting the mast assembly relatively to the main frame of a truck. Thus, the load carriage in the particular truck is mounted, as was earlier outlined, for elevating movement on a mast. The mast, as was also outlined, is adapted to be tilted by a so-called tilt ram, and therefore, the tilt ram is subjected to an increment of the weight of the load. The inventor Carliss has placed, within the functional structure of the piston of the tilt ram, a weight-sensitive element that yields under this load increment, and therefore can sense an overload. This sensing is adapted to actuate a switch for stopping the lifting operation of the truck. Actually; the sensing mechanism can also actuate an alarm, and even render inoperative the traction motor of the vehicle.

While the mechanism shown by Carliss is quite effective, it nevertheless, is costly, very difiicult to adjust, and may be easily damaged severely in usage. This is due partly to the fact that the sensing mechanism is embodied in a structure that actually accepts the load. It is the theory of the invention that I shall disclose herein, that the sensing of the load be not accomplished within the body of an element that itself accepts the load. In my inventive concept, I measure the deformation of a part of the frame of the truck that is subjected to the load through an element that accepts the load, relatively to a part of the frame that in no manner is subjected to the load. In other words, my invention, as will be made apparent shortly, measures deformation of a part of the main frame by a load, against a part of the main frame that is so structurally spaced from the frame part being deformed that it is functionally ef fective to measure the deformation caused by the load.

There will be found also in the prior art, structures that utilize the pressure in the hydraulic system of the tilting ram or the lifting ram for the mast, to sense an overload. It will be obvious that in a system of the particular class, it is the actual load-accepting medium, in this case the hydraulic fluid of the ram, that is the sensing element. Again, we have the same direct relationship between the load and the sensing mechanism that is found in the Carliss patent. Further, while utilizing the hydraulic fluid for the particular purpose will undoubtedly yield an operative structure, it will nevertheless be appreciated that translation of the hydraulic pressure into means for stopping the operation of the traction motor or a motor for operating the lift pump that supplied hydraulic fluid to the lifting mechanism or the tilting mechanism as the case may be, is relatively costly and is difficult to maintain in effective operation. in any event, it is obvious that in the hydraulic system described, we do not find the theory of operation involved in the concept that l have outlined broadly, and which will be described presently in detail.

It has been proposed also that overload sensing be obtained by the utilization of an electrical strain guage. A Pien US. Pat. No. 3,0S9,7 l0 shows such a guage. There, strain is developed between parts of a fork on which a load is applied. Thus, in the Pien strain guage, it is the actual force applied to the load-lifting member itself that is utilized in the sensing of the overload. Therefore, in the utilization of the strain guage as in Pien, not only do we not have the effective concept of my invention, but we also have present the extreme difficulty of translating the sensing by the strain guage into the actual physical movement of 'a switch or other control means or a signal as the case may be. Thus, as is discussed in the Pien patent, a wheatstone bridge and other means are required. This is all quite costly and difficult to maintain in effective operating condition on an industrial truck.

SUMMARY OF INVENTION As already outlined, a basic feature of my invention resides in utilizing for sensing, the deformation or strain of one part of a frame subjected to strain or deformation by a load, with respect to another part of the frame that is not subjected to such strain or deformation by the load.

As a particular feature of the invention, the two parts of the frame I utilize for my purposes, are spaced structurally from one another so that it is not possible for the deformation or strain of one part to reach the other part.

As a further feature of the invention, 1 utilize the application of the load to a ram, preferably the tilt ram of an industrial truck, and the deformation of the main frame that is caused by the acceptance of the load by this ram, as the means for operating my system for detecting overload. As a detailed feature of the invention, l mount the tilt ram on a part of the main frame that will yield in a particular manner, preferably through slight deflecting movement in a particular direction when the tilt ram is under load, and I utilize means extending between this ram support part of the frame and a part of the frame that is structurally spaced from the load and will not yield, for detecting the deflection caused by the load.

As a particular detailed feature of the invention, I utilize a form of movement multiplying mechanism extending between the deflecting part of the main frame and the nondeformable or nondeflecting part of the main frame. Thus, the ram support, adapted to be deflected by the strain of the ram under load, will actually yield elastically and in yielding and in moving through this yielding, will move one part of a lever mechanism, which will bring about considerable movement of a controlling portion of the lever mechanism, and it is through this movement of the controlling portion of the lever mechanism, that a switch or indicator or any other suitable means will be actuated to give that type of control that I require.

l have thus outlined rather broadly the more important features of my invention in order that the detailed description thereof that follows may be better understood, and in order that my contribution to the art may be better appreciated. There are, of course, additional features of my invention that will be described hereinafter and which will form the subject of the claims appended hereto. Those skilled in the art will appreciate that the conception on which my disclosure is based may readily be utilized as a basis for the designing of other structures for carrying out the several purposes of my invention. It is important, therefore, that the claims be regarded as including such equivalent constructions as do not depart from the spirit and scope of my invention, in order to prevent the appropriation of my invention by those skilled in the art.

BRIEF DESCRIPTION OF THE'DRAWINGS Referring now to the drawings:

FIG. I is an elevation of a typical industrial truck to which my invention may be applied.

FIG. 2 is an elevation of the main frame of a typical industrial truck of the type illustrated in FIG. 1.

FIG. 3 is a plan view of the frame shown in FIG. 2.

FIG. 4 is an elevation of a control casing that is adapted to be applied as by bolting or welding to the main frame of FIG. 2

FIG. 5 is a view taken along line 5-5 of FIG. 4 showing a part of the front of the casing of FIG. 4.

FIG. 6 is a detail taken along line 6-6 of FIG. 5.

FIG. 7 shows the control casing of FIG. 4 assembled to the main frame of FIGS. 3 and 4, and with the overload-detecting mechanism in place.

FIG. 8 is a view taken along line 8-8 of FIG. 7 and shows the movement-multiplying mechanism.

FIG. 9 is a view taken along line 9-9 of FIG. 8.

FIG. 10 is a diagrammatic sketch of the electrical control circuit of my invention.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring now more particularly to the drawings, a typical truck to which my invention may be applied, is shown in FIG. II. There, those skilled in the art will see that the load carriage is in the form of load forks 10 that are adapted for vertical movement on a mast embodying movable uprights III and relatively fixed uprights I2. The manner in which the forks 10 are lifted relatively to the uprights Ill and I2 is not illustrated, because these means may be of any type well known in the art. As shown in the Carliss patent to which I have referred, these means are usually a hydraulic ram, shown in my drawings in the form of an arrow R. The ram R will impart vertical lift to the carriage I0 and the movable uprights III in a standard manner.

The relatively fixed uprights 12 of the mast are adapted for pivotal mounting, generally on a bearing that is formed on the forward traction unit, as is standard in this art. In the Carliss patent, the mast assembly is shown mounted on pivots carried by the traction unit, but in the truck I have illustrated, the uprights 12 are formed with brackets 13 through which they are mounted in a standard manner for rotation about suitable bearings 14 on the traction axle.

The truck of FIG. I is shown with forward wheels 15 that are traction wheels carried by the traction unit on which the mast assembly is mounted. Wheels 16 are trailing wheels, and at 17 there is shown a battery that is used in a truck electrically driven. If the truck is actuated by an internal combustion engine, that engine will be mounted where the battery I7 is placed.

At I8 there is a counterweight to which I have referred. This counterweight will balance any load that may be placed on the forks of the carriage I0 so as to prevent the tilting ofthe entire truck about the forward traction wheels I5 as a fulcrum. The weight of the counterweight will naturally be calculated by its distance from the axis or the fulcrum about which the tilting moment will be effective, and also the general load rating of the truck. Any overload on the forks, will naturally bring about the lifting of the wheels I6, and the possibleoverturning of the truck. It is not important to refer in more detail to the parts I have described, as these are standard in the art.

For tilting the mast assembly about its mounting at M, I utilize a pair of hydraulic rams, one of which is designated by reference numeral 20 and is probably best shown in FIGS. I and 7. The piston of the ram 20 is designated by reference numeral 21 and it is pivoted at 22 to a bracket 23 that is an integral part of the fixed upright 12. Obviously, the rams 20 can effect rearward tilting of the mast I2 and the forks together with the load to better position the load center of gravity for travel. Of course, the rams 20 will be stressed in proportion to the weight of the load, and therefore the supports on the main frame for the rams will be stressed. It is this stressing of the main frame by the load on one ram 20, and the deflection caused by this stress, that is utilized by me for providing an overload-detection system, all as will be set forth in detail presently.

Referring now to FIGS. 2 and 3, I show the main frame of the truck to which my invention is applied. It will be noted that this main frame utilizes two vertical side steel plates 25 and 26, these plates being held assembled to one another by several transverse members, generally by welding so that the result is an integral extremely rigid main frame. In FIG. 2, one of the side plates 25 is shown in elevation. It will be noted that extending between the plates 25 and 26 is a horizontal plate 27 welded to the upper end of a vertical transverse plate 28 that is also welded to plates 25 and 26. Welded to the plate 28 are two horizontally extending support brackets 29 and 30. The brackets 29 and 30 are utilized for the mounting of a standard traction unit on the ends of which are supported the traction wheels 15. For this purpose each bracket 29 and 30 is formed with a bearing surface 3H that cooperates with a bearing surface 32 formed on a cap 33. Each cap is secured to its particular bracket by a pair of heavy bolts 34 as is well known in this art. The particular mechanism is conventional and is described broadly for the purpose of outlining the general construction of a truck to which my invention may be applied.

While many industrial trucks use but one ram for tilting the load rearwardly, I prefer to use two rams such as the ram 20 to which I have alluded. Each ram is naturally mounted on the main frame. I shall describe now the'supports for the rams. On plate 27 a pair of bearing blocks 35 are welded at one side of the main frame, and a pair of bearing blocks 36 are welded at the other side of the'main frame. Each pair of these bearing blocks has a pair of opposed caps 38 screwed thereto by bolts 39 and forming a pair of spaced bearing openings 37. Each of the rams 20 has opposed lugs 20a at one end thereof that fit into the bearing openings 37 for supporting the rams 20 relatively to the bearing blocks 35, 36. It is obvious, that through the bearing blocks 35, 36 and lugs 20a the forces exerted against the rams 20 by the load will be accepted.

The particular construction of the bearing blocks 35 and as, is not important insofar as the operation of my invention is concerned, since it is obvious that the rams need only be mounted on bearings in such a manner that the bearings will accept the forces applied thereto in the handling of the load. In FIG. 2 the arrow vector 46 extends along the axis of a ram secured at its ends to the mast 12 at point 22, and to the truck at the bearing 37 of a pair of blocks 35, and indicates the line of stress of the ram.

As those skilled in the art will appreciate, any stresses on the rams due to the load, will be accepted by the bearing blocks 35 and 36, and the bearing blocks together with the plate 27 will deflect under the stress of the load. While this deflection will naturally be extremely slight, I have developed a mechanism for utilizing this deflection.

It will be noted in FIGS. 2 and 3 that each of the plates 25, 26 has welded thereto a pair of brackets W and All. A control casing 45, best shown in FIGS. 1, 4 and 5, is mounted at the forward end of truck main frame through these brackets. The control casing 45 is preferably fabricated from sheet metal bent into the shape illustrated in the drawings and suitably reinforced. At its upper end it supports a steering wheel such as shown in FIG. 1, and generally instruments will be mounted thereon in a position where they may be viewed by the operator, all as is standard in this art.

In the construction I have shown, at the lower end of each side of the control casing 45, there are holes 40a and 41a adapted for coaction with the holes shown in the brackets 40 and 41 in FIG. 2. Through suitable rivets or bolts, it is obvious that the control casing 45 may be secured to the brackets 40 and 41 as seen in FIG. 7. While it then becomes an integral part of the main frame of the truck, it nevertheless is functionally spaced from the bearing blocks 35 and 36 and is not in any way subjected to the stresses accepted by bearing blocks 35, 36 and plate 27. It is this relationship of casing 45 and the bearing blocks, that makes possible the effective operation of my invention.

As well shown in FIGS. 5 and 6, a suitable fulcrum pin 50 may be secured to the bottom of the control casing, by bolting to the casing a plate 51 to which the pin 50 may be welded.

Also shown secured to bottom of the control casing 45 is a bracket 52, to which may be secured a switch mechanism that will be described presently.

Referring now more particularly to FIGS. 7, 8 and 9, in order to amplify any movement of the one bearing block 35 illustrated in FIG. 7, l weld to that block a rod 55 so that the rod will move integrally with the bearing block 35 as that block moves under the influence of the forces exerted against the ram 20. The end of the rod 55 is bored and tapped as shown in dotted lines at 56 for-a cap screw 57. A multiplying lever 58 is bored for; the passage of the cap screw 57, so that the cap screw when entered into the threaded opening 56 of the rod 55 may mount the lever 58 for rotation about the axis of the cap screw 57 as well as the axis of rod 55. The cap screw 57 is further shouldered at 59 so that its entry into the tapped opening 56 is limited, and it will therefore function very effectively to hold the lever 58in position for free swinging motion.

While the lever 58 may swing relatively to the rod 55, it is obvious, also, that it will move bodily with the rod 55 as that rod moves because of deflection of the bearing block 35. The lever 58 extends at one side beyond its mounting on the cap screw 57 so that one surface thereof may be applied to the fulcrum pin 50, which it will be remembered, is welded to the control casing 45 as shown inFlGS. 5 and 6.

A switch 60 is secured to the control casing 45 by means of the bracket 52 to which reference has already been had. This switch 60 is of that type in which, when its plunger 61 is in its position of FIGS. 8 and 9, a circuit is made through contacts within the switch body. On the other hand, when the plunger 61 is pressed inwardly the circuit is broken. Of course, the switch can be ofa diflerent construction, and the arrangement of the switch relatively to the lever 58 could be such that when the lever is pivoted, the plunger 61 is projected by a spring in order to open a circuit. In either construction, merely adjusting the switch body 60 relatively to the bracket 52, places the plunger 61 into exact relationship relatively to the multiplying lever 58, while the circuit in the switch body 60 is closed. With this arrangement, any rotation of the switch lever in the direction of the arrow 63 in FIG. 8 will naturally press the plunger 61 inwardly relatively to the switch body 60 so as to break the electrical circuit. 1 shall presently describe the circuit in some detail.

Referring now to FIG. 7, it will be seen that when the ram is accepting the weight of the load on the carriage and the upright 12, the bearing block 35 shown in FIG. 7 will tend to deflect with plate 27 in the direction of the arrow 64. This deflecting of the bearing block 35 will cause the rod 55 to move as shown in FIG. 8 in the direction of the arrow 65. Since the fulcrum 50 is fixed, it is obvious that the lever 58 will swing counterclockwise and will press the spring-pressed plunger 61 inwardly relatively to switch body 60. This movement of the plunger 61, as was earlier outlined, will bring about the opening of a circuit within the switch body 60. As has also been emphasized, the positions of the fulcrum 50 and the switch body 60 can readily be reversed relatively to the multiplying lever 58, if another type of switching action is desired. It is exceedingly important to be able to adjust effectively and accurately the position of the switch body 60 and its plunger 61 relatively to the multiplying lever 58 so that there will be effective contact between the plunger 61 and the multiplying lever 58 when there is no stress exerted against the bearing block 35. The arrangement that l have conceived and utilized and illustrated, is most effective for the particular purpose and for that reason has been adopted by me.

Referring now to FIG. 10, I show there an electrical diagram for a typical control circuit utilizing the concept of my invention. In the diagram, all solenoids are shown energized so that a circuit is completed from the battery 70 to a pump motor 71. The pump motor 71 drives a pump that is not shown, for supplying fluid under pressure to the elevating ram R of my truck. As was already set forth, the ram R is of standard construction and operates to lift the load forks in a conventional manner.

If during operation of the pump motor 71 there is an overload so that the bearing block 35 is deflected, the rod 55 will move in the direction of the arrow 65 in FIG. 8 and the multiplying lever 58 will rotate counterclockwise. This will naturally move plunger 61 to open a circuit at switch 60 through the contacts 73 thereby breaking the circuit through the solenoid ofa relay 74 and the circuit of the solenoid ofa relay 75, so that the contacts 74a and 750 may open. Relay 74 has a dash pot 74b or similar time-delay device which delays the opening of the contacts 74a for a short period after the solenoid 74 has been deenergized. A double dash pot 75b functions in a similar manner relatively to contacts 75a. If the overload is not relieved during this delay, contacts 74a open and break the circuit to a motor control relay 76 so that the contacts 76a may open to stop operation of the motor 71, and therefore, stop lifting of the load forks by the ram R.

The delay in opening the contacts 74a provided by the dash pot 74b prevents the stopping of the motor 71 by a momentary overload such as may be caused by inertia forces acting momentarily to increase the effective weight of the load.

When the overload is relieved, the contacts 73 close again, thereby completing a circuit to relay 75 to energize the solenoid thereof and to close the contacts 75a of relay 74. Dash pot 75b delays the closing of the contacts 750 for a short period after the solenoid of relay 75 has been energized. This delay prevents starting of the motor 71 through action of relays 74 and 76 by inertia forces acting momentarily to decrease the effective weight of the load.

The control circuit, which is similar to that found in the Carliss patent, may also include warning devices such as a horn 80, and the light 81, the circuits through which are closed by a second series of contacts 76b when the circuit of the motor 71 is opened. With such an arrangement, not only will lifting of the load be stopped, but an alarm will be sounded and an indicator light will be flashed.

I believe those skilled in the art will now understand the nature of my contribution.

What I claim is:

1. In an industrial truck having a frame, a mast pivotably mounted on said frame adjacent the front of said truck for fore-and-aft tilting movement, load-supporting means mounted on said mast for supporting a load in front of said mast whereby a moment is applied to said mast tending to tilt said mast forwardly, a ram, means connecting one end of said rarn to said mast, and a ram support connecting the open end of said ram to said frame, the improvement comprising, means mounting said ram support relative to said frame so that the support is deflected relatively to said frame upon stressing of said ram by a load on said load member, a fulcrum member forming an integral part of said frame while structurally so spaced from said ram support that said fulcrum member will not be subjected to the deflection of said ram support relatively to said frame when the ram is so stressed, a movement-multiplying lever actuated by the deflection of said ram support and bearing against said fulcrum member about which said lever is pivoted and means actuated by of saidlever. v

2. In the combination ofclaim l, the featurethat said movement-multiplying lever actuates a switch upon a predetermined degree of deflection of said ram support relatively to said structural member.

3 In the combination of claim 1, the feature that said lever is pivoted on a portion of said ram support in a position so that a part of the lever on one side of the pivot bears against said fulcrum member, and said means actuated by said lever is actuated by a second part of said lever.

4. In the combination of claim 3, the feature that said fulcrum member and second part are-at opposite ends of said lever and said portion is between said fulcrum and second the pivoting movement part.

5.- ln the combination of claim 1, the feature that said lever is pivotably mounted on a bearing on said ram support.

6. The combination of claim 1 further comprising a timedelay element operatively associated with the means actuated by said multiplying mechanism to prevent actuation thereof until said deflection has existed for a predetermined period of time.

7. In the combination of claim 5 in which said bearing is positioned substantially perpendicular to the longitudinal axis of said ram and said lever is pivoted in a plane perpendicular to said axis of said bearing. 

1. In an industrial truck having a frame, a mast pivotably mounted on said frame adjacent the front of said truck for foreand-aft tilting movement, load-supporting means mounted on said mast for supporting a load in front of said mast whereby a moment is applied to said mast tending to tilt said mast forwardly, a ram, means connecting one end of said ram to said mast, and a ram support connecting the open end of said ram to said frame, the improvement comprising, means mounting said ram support relative to said frame so that the support is deflected relatively to said frame upon stressing of said ram by a load on said load member, a fulcrum member forming an integral part of said frame while structurally so spaced from said ram support that said fulcrum member will not be subjected to the deflection of said ram support relatively to said frame when the ram is so stressed, a movement-multiplying lever actuated by the deflection of said ram support and bearing against said fulcrum member about which said lever is pivoted and means actuated by the pivoting movement of said lever.
 2. In the combination of claim 1, the feature that said movement-multiplying lever actuates a switch upon a predetermined degree of deflection of said ram support relatively to said structural member.
 3. In the combination of claim 1, the feature that said lever is pivoted on a portion of said ram support in a position so that a part of the lever on one side of the pivot bears against said fulcrum member, and said means actuated by said lever is actuated by a second part of said lever.
 4. In the combination of claim 3, the feature that said fulcrum member and second part are at opposite ends of said lever and said portion is between said fulcrum and second part.
 5. In the combination of claim 1, the feature that said lever is pivotably mounted on a bearing on said ram support.
 6. The combination of claim 1 further comprising a time-delay element operatively associated with the means actuated by said multiplying mechanism to prevent actuation thereof until said deflection has existed for a predetermined period of time.
 7. In the combination of claim 5 in which said bearing is positioned substantially perpendicular to the longitudinal axis of said ram and said lever is pivoted in a plane perpendicular to said axis of said bearing. 